Terahertz waves are undeveloped frequency resources having a bandwidth from 100 gigahertz (GHz) to 10 terahertz (THz) and correspond to an intermediate area between infrared light and a millimeter wave in an electromagnetic spectrum. Terahertz waves are in an unexplored technical field recognized as a kind of a terahertz gap due to a very high barrier to entry at a current technology level. A terahertz wave technology was mainly in an optical field at first. However, with development of nano-level electronic device/material technologies, the terahertz wave technology has been applied as a combination of an optical engineering technology and an electronics engineering technology.
In the electronics engineering technology, research on a passive element, for example, a resonant tunneling diode (RTD) and a schottky barrier diode (SBD), has been actively conducted. Recently, III-V heterojunction bipolar transistor (HBT) and high-electron-mobility transistor (HEMT) devices have succeeded in an access to a block frequency of 1 THz, which allows a sub-THz operation. In the optical engineering technology, development of devices, for example, a photoconductive switch, an optical rectification, a difference-frequency generation (DFG), an optical parametric, terahertz-quantum cascade lasers (THz-QCL), and uni-traveling-carrier photodiodes (UTC-PD), have been actualized to advance a terahertz technology.
Current nano-transistor technologies have been continuously downscaled to 20 nanometers (nm) for achieving an increased operating frequency. However, an operation at a band of 500 GHz or more may be restricted despite a channel reduction in a transit-mode. A plasma wave transistor (PWT), as a new concept element provided to solve this issue, may operate at a velocity corresponding to 10 to 100 times of a transit-mode electron drift velocity using a plasma wave defined as a space-time oscillating wave of a channel electron density. Research on a PWT for terahertz emission and detection devices operating in a frequency domain higher than a block frequency of a transistor based on a plasma resonance phenomenon of a two-dimensional (2D) channel electron density has been conducted all over the world to be used as a technology for filling the terahertz gap.
Since 1993 when Michael Shur, a professor at Rensselaer Polytechnic Institute (RPI) in the United States proposed for the first time, research on implementation and application of a terahertz emission and detection device using the PWT has been conducted in universities in the U.S., Japan, and Europe for about 20 years. However, there is still a technical difficulty in evaluating a terahertz device and properties of the terahertz device at a commercialization level.
In Terahertz Emitters, Detectors and Sensors: Current Status and Future Prospects, M. Ghanashyam Krishna, Sachin D. Kshirsagar and Surya P. Tewari, intech., and Terahertz Resonant Detection by Plasma Waves in Nanometric Transistors, F. Teppe, A. El Fatimy, S. Boubanga, D. Seliuta, G. Valusis, B. Chenaud and W. Knap, Proceedings of the 13th International Symposium on UFPS., a technology for reaching a terahertz range using a resonator for a plasma wave, a correlation between a frequency of the plasma wave and a drain-to-source current, and a relationship between a plasma wave velocity and a drift velocity are theoretically explained.
A method of evaluating a performance of a PWT based on the theory of the above prior arts has been filed by the present applicant and registered with Korean Patent No. 1521116. The above patent relates to a resonant PWT and has a feature of evaluating an application characteristic as a terahertz emitter.
The present applicant has provided a suspended channel PWT (referred to as an “SC-PWT”) that overcomes a disadvantage of an existing resonant PWT, and filed Korean Patent Application No. 10-2014-0193098 which is directed to a configuration of an emitter and a detector based on the above configuration.
Since the SC-PWT or a suspended channel plasma wave device (referred to as an “SC-PWD”) is different from a resonant PWT in basic characteristics, an evaluation methods according to a related art is inadequate for evaluation of a characteristic of a device. Accordingly, there is a need for a new evaluation method.